1. Field of the Invention
This invention relates to laser drawing technology used in semiconductor manufacturing, micro-processing, and computer hologram manufacturing, etc.
2. Description of the Related Art
A conventional laser drawing apparatus is described with reference to FIG. 5. The laser drawing apparatus diagrammed in FIG. 5 is for manufacturing reticles (photo-exposure plates) used in the manufacture of integrated circuits.
A photographic dry plate 504 made by coating a glass substrate with a photosensitive material is placed on an XY turntable 501. The XY turntable 501 can be moved in the x axis direction by an air slider 502 and in the y axis direction by an air slider 503, driven by linear motors (not shown) contained inside the air sliders 502 and 503.
Meanwhile, a laser beam 112 output by a gas laser is transmitted through an optical modulator 103 and advances to a mirror 102. The transmitted light intensity of the laser beam 112 can be modulated by the optical modulator 103, and here is a value that is either some prescribed light intensity or zero light intensity. The beam reflected by the mirror 102 is reflected by a mirror 104, condensed by an object lens 105, and focused on the photographic dry plate 504.
In actual practice, when drawing on the photographic dry plate 504 with the laser beam 112, the air sliders 502 and 503 are controlled in accordance with the pattern being drawn, and the desired pattern is exposed on the photographic dry plate 504 while the laser beam 112 is repeatedly transmitted and interrupted by the optical modulator 103 in conjunction with that control. Ordinarily, the method employed is that of drawing the outline of the pattern, and then filling in the outline, as when drawing with a plotter.
Another proposed method is one wherein laser drawing is performed at high speed using a turntable and sliders, employing an optical disk mastering process, as described in Japanese Patent Application Laid-Open No. S59-171119. An example of a pattern drawn is given in FIG. 6.
Here, drawing is done with the turning speed of the turntable and the moving speed of the sliders held constant, with the turntable turning about a center at a center point 601. The resist coat surface on the glass plate is divided into dots at polar coordinates (rm, xcex8n) Exposure is effected while modulating the light on the basis of information as to whether to expose or not expose the dots at each pair of coordinates.
However, when the XY table type laser drawing apparatus diagrammed in FIG. 5 is used in finely drawing complex patterns, the distance traveled each time by the air sliders 502 and 503 in the x and y directions becomes very minute, making it necessary to effect acceleration and deceleration during that time. Accordingly, the average movement speed becomes rather slow, whereupon the drawing time becomes long. Also, when filling in the interior with laser irradiation after forming the outer contour of the pattern, the amount of reciprocal motion becomes considerable, and, when drawing at high speed, not only are considerable loads imposed on the linear motors, but, simultaneously therewith, the reactions of the XY table 501 during acceleration and deceleration themselves become a cause of vibration, whereupon positioning precision and speed precision decline.
With the scheme diagrammed in FIG. 6, moreover, the turning speed of the turntable is fixed during drawing, wherefore the length in the circumferential direction of a dot 606 on the inner circumference is shortened, while the length of a dot 607 on the outer circumference is lengthened. Accordingly, the resolution of the drawn pattern 603 declines at the outer circumference, and precise patterns cannot be drawn.
With the problems noted in the foregoing in view, an object of the present invention is to provide a laser drawing apparatus and laser drawing method wherewith fine patterns can be drawn at high speed and uniform fineness.
In order to resolve the problems discussed in the foregoing, the laser drawing apparatus of the present invention comprises a turntable whereon is mounted material to be processed and which turns said material, a slider capable of linear movement, a laser that serves as a light source, an optical system for condensing laser light to form a laser spot on the material to be processed loaded on the slider, an optical modulator for varying the light intensity of the laser spot, and an oscillator for generating a clock signal for synchronizing control signals input to the optical modulator. Here, if r is the distance of the laser spot formed on the material to be processed from the turning center of the turntable, fc is the rotational frequency of the turntable, Wd is the length in the radial dimension of the laser spot formed on the material to be processed, and N is a positive integer, then the clock signal frequency fd is adjusted to fd=rNfc/Wd.
For a preferred aspect of the present invention, moreover, in the configuration described above, if r is the distance of the laser spot formed on the material to be processed from the turning-center of the turntable, fc is the rotational frequency of the turntable, Wd is the length in the radial dimension of the laser spot formed on the material to be processed, xcex8 is the center angle in a fan-shaped area being drawn, and N is a positive integer, then the clock signal frequency fd may be adjusted so that fd=2xcfx80rNfc/xcex8Wd.
It is preferable, moreover, that the turntable rotational frequency fc and the clock signal frequency fd be constant.
The configuration may also be made so that the turntable rotational frequency fc is constant, the oscillator is synchronized with the rotational frequency fc, and the clock signal frequency fd is varied according to the radius r.
It is also permissible to make the clock signal frequency fd constant, to further provide a signal generator for generating signals for controlling the rotational frequency fc of a spindle motor that is a drive source for the turntable, and to synchronize the clock signal frequency fd with the signal generator and vary that frequency according to the radius r.
As an embodiment aspect of the present invention, where the material to be processed is a blank plate coated with a photosensitive material, laser drawing is performed on that photosensitive material.
In the laser drawing method of the present invention, laser light is condensed to form a laser spot on revolving material to be processed, control signals input to an optical modulator are synchronized by a clock signal obtained from an oscillator, the clock signal frequency fd is adjusted so that fd=rNfc/Wd where r is the distance of the laser spot formed on the material to be processed from the turning center of the material to be processed, fc is the rotational frequency of the material to be processed, Wd is the length in the radial dimension of the laser spot formed on the material to be processed, and N is a positive integer, the light intensity of the laser spot is varied by the optical modulator in synchronization with the control signals, and a discretionary pattern is laser-drawn on the material to be processed.
In a preferred aspect of the present invention, laser light is condensed to form a laser spot on revolving material to be processed, control signals input to an optical modulator are synchronized by a clock signal obtained from an oscillator, the clock signal frequency fd is adjusted so that fd=2xcfx80rNfc/xcex8Wd, where r is the distance of the laser spot formed on the material to be processed, fc is the rotational frequency of the turntable, Wd is the length in the radial dimension of the laser spot formed on the material to be processed, xcex8 is the center angle in a fan-shaped area being drawn, and N is a positive integer, the light intensity of the laser spot is varied by the optical modulator in synchronization with the control signals, and a discretionary pattern is laser-drawn on the material to be processed.